Gem grinder with approach control means

ABSTRACT

A gem polishing machine having a rotatable flat lap with a dop mounted above the lap and movable to polish the gem on the abrasive surface of the lap. Sensor means are provide to signal force applied to the gem and with an ultimate stop to end the cycle.

United States Patent [191 Bean 1 1 Sept. 2, 1975 [54] GEM GRINDER WITHAPPROACH 2,971,263 2/1961 Rockafellow 51/l69.75 X CONTROL MEANS3,724,138 3/1973 lshikawa 5l/165.8

[76] Inventor: Philip D. Bean, 3253 S. 162nd St.,

Seattle, Wash. 98188 [22] Filed: Jan. 18, 1974 [21] Appl. No: 434,415

[52] US. Cl. 5l/125.5; 51/165.75; 51/165.8; 51/229 [51] Int. Cl. B24B9/16 [58] Field of Search 51/165 R, 165.75, 165.77,

[56] References Cited UNITED STATES PATENTS 2,829,472 4/1958 Salzer51/229 X Primary Examinerl-larold D.. Whitehead Attorney, Agent, orFirmRoy E. Mattern, Jr.

[5 7] ABSTRACT means are provide to signal force applied to the gem andwith an ultimate stop to end the cycle.

10 Claims, 8 Drawing Figures PATENTEUSEP 2197s 3, 9 02,283

sum 1 (IF g FORCE a4 AMPLIFIER 82 FIG. 4

PATENTEBSEP 2|97s 3. 902,283

SHEET 2 UF 2 FACET CUTTING METER DEVIVCE LIGHTS DOPSTICK STOP DIGITALTRANSDUCER AMPLIFIER AUD'BLE OTHER. FIG 5 GEM GRINDER WITH APPROACHCONTROL MEANS BACKGROUND OF THE INVENTION Previously, when precision gemfaceting machines or other machines were being used by skilled craftsmento cut and/or to polish diamonds and/or other valuable gem stones, thegem stones were mechanically positioned in predetermined selected indexposition for movement toward the surface of an abrasive turntable, sofacets could be formed in a perfect geometric arrangement. During suchmovement, either a mechanical control assembly or a manual pressureassembly was used to urge the gem stone against the abrasive cuttingsurface until a limit actuator means, such as electrical contacts or amechanical stop, were contacted Therefore, the precision of a facetingor shaping operation has been dependent on the sensitivity andrepeatability of these limit positioning or limit actuating means. Evenslight unwanted tolerances or movements or deflections created asmechanical pressures or forces over-stress the limit positioning means,may re sult in flaws being created in cut and/or polished gems.Therefore in the past, the gem cutter has had to rely on his or herfinely developed finger touch and/or to use a hearing sound cuttingmethod to cut and/or polish gem surfaces or shapes. Extensive andrepeated careful inspections, therefore were frequently undertaken asthe cutting and/or polishing was being performed, in order to staywithin limits of polishing or cutting. The use of most stops, in thepast, have created an abrupt signal which does not enhance thecraftsmans sense of feel. Moreover, there are variances in pressures required, as hard and soft faces of the same gem stone are being cut orpolished during final stages of polishing. Therefore there has been aneed to create a greater sensitivity to both pressure and movementduring concluding cutting of rough or final forms and polishing, andthis electro-mechanical position sensing subassembly incorporatingstrain gages has been developed.

SUMMARY OF THE INVENTION In several embodiments electro-mechanicalposition sensing subassemblies, incorporating strain gages and- /orproximity sensor components, are provided to create the greatersensitivity to both pressure and movement that is necessary duringconcluding cutting of rough or final forms and polishing of surfaces ofgems, when using machinery, such as faceting machines or gem faceters,When these embodiments are installed and observed, forces of one gram orless are easily monitored, and movements as small as a few or, five orless millionths of an inch are readily detected. In one embodiment, thecircuitry of the strain gages in a wheatstone bridge arrangement iscoupled with an electronic amplifier read out meter to present acontinuous calibrated visual display or read out during the last fiveten-thousandths of an inch of movement of the gem stone toward thecutting wheel, skaif, or lap, and before the final or ultimatemechanical stop is reached. Therefore the approach to the ultimate stopis indicated, rather than the abrupt arrival at the ultimate stop. Inthis way, the electro-mechanical position sens ing and indicatingsubassembly, complements and increases the operators control and his orher sense of touch as he or she views, for example, the needle of anelectronic amplifier read out meter swinging toward the indicated fullor ultimate stop position while he or she is removing very small amountsof material from the diamond, or gem stone giving him or her a veryaccurate indication of the speed at which the ultimate stop limit pin isbeing approached.

In another embodiment, proximity sensor components are incorporated, inlieu of strain gages, in circuitry which alters the electrical energydelivered to electronic units, such as a gage having an easily observedsweep hand or needle. These embodiments, using either the strain gagesor proximity sensors, are arranged for use during the concluding shapingof either rough or finished facet surfaces. Also, both of theseembodiments, with necessary modifications, become additional embodimentswhich are adapted to being installed at another position on machinery,such as faceting machines and gem faceters, for use during theconcluding shaping of either rough or finished marquis, pear, oval,heart, antique cushion, emerald and other shapes.

DRAWINGS OF PREFERRED EMBODIMENTS FIG. 1 is a perspective view ofa gemcutting, shaping, and polishing machine, referred to as a facetingmachine, equipped with the electro-mechanical position sensing andindicating subassemblies;

FIG. 2 is a partial side view of the faceting machine indicating therelationship of the movement of the end of the dop stick holding the gemstone during machine operations, to the movement of the needle on theindi cating read out meter of the electromechanical position sensing andindicating subassemblies;

FIG. 3 is a partial transverse view with portions sec tioned to indicatehow the dop shaft or arm housing at its end opposite to the dop stickholding the gem stone, is moved against the pick up .and sensingelements of the electro-mechanical position sensing and indicatingsubassembly which incorporates strain gages mounted on a cantileveredbeam;

FIG. 4 is a schematic circuit diagram of the electromechanical positionsensing and indicating subassembly utilizing strain gages;

FIG. 5 is a schematic block diagram indicating how a facet cuttingmachine or faceting machine with an electro-mechanical position sensingand indicating subassembly, centering on the use of a dop shaft or armstop transducer, using, as necessary, an amplifier, may selectively bematched to a meter, light system, digital read outs, audible soundgenerators and/or other ob servable indicators to aid the operator ofthe gem forming machine or faceting machine during production of aperfect gem;

FIG. 6, is a partial perspective view of the gem cutting, shaping andpolishing machine, referred to as a faceting machine, indicating anotherembodiment of components of the electro-mechanical position sensing andindicating subassemblies used in conjunction with control cams, whichare in turn employed to control cutting and polishing marquis, pear,oval, heart, antique cushion, emerald and other shapes;

FIG. 7 is a partial transverse view, with portions shown in section, ofhow this dop shaft or arm stop transducer is mounted with its straingages, and the subassembly is employed during the cutting and polishingof marquis, pear, oval, heart, antique cushion, cmerald and othershapes;

FIG. 8 is a partial transverse view, with portions shown in section, ofhow, in lieu of a deflection beam with strain gages, a proximity sensoris utilized to indicate the small movements occurring as the dop shaftor arm is concluding its intended movement, either during the early orfollow on cutting or polishing steps, to create, for example, theperfectly formed facet on a gem.

DESCRIPTION or THE PREFERRED EMBODIMENTS The various illustratedembodiments of the electromechanical position sensing subassemblies areshown in conjunction with gem cutting and polishing machines 22generally referred to as faceting machines, shown in FIG. I, whichposition a gem stone 24, for precise, repeatable angle approaches to arevolving flat rotatable disk 26, known as a lap. It has a selectabletype of abrasive surface materials, which together are also referred toas a cutting wheel or skaif. A valuable gem stone 24 is secured to a dopor dop stick 28 and then by a collect or chuck subassembly 30 to a dopspindle housing assembly 32 and in turn to the angular positioned pivotbody 34. A curved support 36 with a radial adjustment protractor scale38, together generally referred to as the protractor 36 slidablyreceives a partially overlapping top housing generally referred to as afacet angle setting assembly or saddle block 40 which rotatably holdsthe pivot body 34, and therefore ultimately pivots the dop 28. Thesaddle block 40 is movable along the protractor 36, upon movement of afacet angle adjusting mechanism, not shown. Also the protractor 36 issecured to a supporting member 42. It in turn is slidably positioned ona vertical adjustment support subassembly 44 equipped with preciseheight adjustment calibration actuators and adjusters 46 utilizingmicrometer height dials, referred to as the micrometer verticaladjustment. Center portions 48 of this vertical support subassembly 44are selectably and firmly mounted to the base 50 in adjustable positionsalong slide retainer 52 of the facet cutting and polishing machine 22,and outer portions 54 thereof slide on the center portion 48. The base50 rotatably supports the splash pan or housing 56 in which the lap 26revolves. The lap mounting spindle or shaft 58 with its securement nut60, is driven below within the base 50 by a drive shaft of an electricmotor and guided in precision bearings, not shown. Also not shown, forclarity, are lights and a subassembly for supplying cutting and polishing liquids to the lap, wheel, or skaif 26.

Approaching a Specified Angle Utilizing Strain Gages As shown in FIG. 1,in this particular embodiment, the eIectro-mechanical position sensingand indicating subassembly 20, uses an electronic amplifier read outmeter 64 to indicate, by movement of a sweep hand or needle 66, theconcluding gram of force and/or the concluding increments of movements,in reference to the motions of the dop or dop stick 28, as, for example,when a first rough cut, or a finishing polishing operation, is beingconcluded in reaching the intended surface or shape, as specified, inreference to the particular forming of a gem 24. This is illustratedfurther in FIG. 2, after the overlapping top housing or saddle block 40is secured at its intended angular position on the protractor 36, thedop 28 and its various supporting subassemblies 30, 32, 34, is pivotedabout its pivotal mounting 68 to the saddle block 40 to cause thecutting or polishing of a gem stone 24, upon the relative movement ofthe lap 26. Then, for example, during the concluding 0.001 inch offorming, in view of the 2X to 1X, pivotal mounting 56 location, the0.0005 inch of movement to the ultimate stop 58 is accurately sensed, asfurther indicated in FIG. 3.

The pivot body 34, which rotatably receives the dop spindle housingassembly 32 and which is pivotally attached to the saddle 40 by usingthe pivotal mounting 68, has a formed protruding abutment 70 whichultimately bears against the cylindrical or pin ultimate stop 72. Yetbefore the firm ultimate contact occurs, there is a range of an initialand adjusting contact made with an adjustable advanced probing pin 74which is movably retained in the stop 72. As shown in FIG. 3, theprobing pin 74, which is a screw, threadably secured in a cantileveredbeam structure 78 mounted within the ultimate stop 72 secured to or apart of the saddle block 40. Mounted on the cantilevered beam structure78 are strain gages 80 which are strained upon the movement of thecantilevered beam structure 78.

As indicated in FIG. 4, the changes in stress of the strain gages 80,create an unbalance in the active circuitry 82 which is sensed andthereafter indicated on the amplifier or read out meter 64, uponmovement of the sweep hand or needle 66.

Approaching a Specified Contour Utilizing Strain Gages Many of the sameelectro-mechanical position sensing subassembly 20, components are alsoutilized during the approach to a specified contour in anotherembodiment used when cutting or polishing a gem stone 24 to obtain aspecific shape, using cams to control the cutting and/or polishingoperations to reach marquis, pear, oval, heart, antique cushion, emeraldand other shapes. In FIG. 6, one of these earns 90 is shown removablysecured near the top of the dop shaft 92. When rotative and pivotalmovement of the dop shaft 92 and dop stick 28 is occurring to form a gemfrom a gem stone 24 to match the cam controlled shape, as the contour ofthe cam is approached, an advanced, retractable plunger 96, protrudingbeyond the ultimate stop structure 98, is first contacted. Ultimate stopstructure 98 in FIG. 7 is secured to or apart of saddle block 40 ofFIGS. 1 and 3. As illustrated in FIG. 7, retractable plunger 96 butts upagainst and contacts the cantilevered beam 100 near its end. Straingages 80 are installed on the cantilevered beam 100 which is fastened toultimate stop structure 98 by means of fasteners 102. The circuitry 82and these strain gages 80 are protected under cover 104, and thecircuitry 82 is utilized in the same way, as illustrated in FIG. 4 toindicate the deflection of the beam 100, etc. The resulting movement ofthe sweep hand 66 on meter 64 is observed by the person forming the gemfrom the gem stone 24 and as a consequence he or she forms the gemperfectly.

Approaching Specified Angles or Contours Utilizing Proximity Sensors Inthe same gem machining environments, the person forming the gem, usingelectro-mechanical position sensing subassemblies, also achieves betterresults when, in lieu of strain gages 80 and circuitry 82, proximitysensors 108 are installed with their circuitry I10, as illustrated inFIG. 8. For example, referring to FIGS.

2 and 8, as the abutment 70 on pivot body 34, with its magneticallyattracted insert 112 moves toward the proximity sensor 108, installed inultimate stop 114, which in turn is secured to or a part of saddle block40, the signals generated are indicated on the electronic amplifier readout meter 64, upon movement of the sweep hand 66. Also, as indicated inFIG. 5, the approach to the ultimate stop may be observed by usinglights, digital readings, audible signals, and/or other signals.

Other Components Noted for Better Understanding in FIGS. 1, 2 and 6,some features, perhaps best referred to as prior art features, areillustrated; however, they are not directly pertinent in reference tothe use of the electro-mechanical position sensing and indicatingsubassembly 20. For example, index lever 116, pivots at 118 to clear itslocking end 120 from the radial facet stops 122 on the index gear 124.Also a precision worm gear device, known as a cheater or splitter, 126is used to turn the dop spindle housing subassembly 32 and thus the gemstone 24 on its own axis, providing further refining adjustments to theradial index of facets.

SUMMARY OF ADVANTAGES When gem cutting and polishing machines also knownas gem faceters, or faceting machines are improved by the additionand/or incorporation of electromechanical position sensing andindicating subassemblies centering on components such as strain gagesand- /or proximity sensors, the following advantages are realized: thefear of overcutting is eliminated; the alignment of the potential facetof the gem to the polishing or cutting surface is accurate; the interiminspection times are greatly reduced with a corresponding decrease infatigue and eyestrain; the operators sense of touch is enhanced givinghim or her a higher degree of sensitivity and more opportunity forrepeatable accuracy; the range of approach via the various means, suchas the meter needle movement, is accurately presented during the givenconcluding cutting or polishing operations, throughout a finite rangebefore an ultimate abrupt mechanical stop is reached, and the rate ofremoval of the material is at the same time well indicated; soundcutting methods no longer need to be practiced; more delicateoperations, free of excessive manual operating forces, are undertaken;moreover, the electromechanical position sensing and indicating subassemblies are readily incorporated into more extensive automatic controlassemblies; and throughout the entire use of these electromechanicalposition sensing and indicating subassemblies, there are the savings intime during the making of repeated precision facet cuts, and there arethe ultimate savings realized by avoiding the spoiling of a gem byovercutting and/or over polishing.

I claim:

1. A gem cutting and polishing machine, comprising:

a. a base;

b. a fiat rotatable disc or lap, mounted upon the base,

for mounting selectable abrasive surfaces;

c. a pivot body support structure, mounted upon the base, comprising inturn;

1. a pivot shaft with axis parallel to the lap plane;

2. an ultimate stop structure;

3. a structure which supports the ultimate stop structure and pivotshaft, and which can be ad justed to control the height of the pivotshaft above the lap and the angle between the lap plane and an axisrunning from the pivot shaft to the ultimate stop structure;

d. a pivot body, mounted rotatably upon the pivot shaft in such a waythat its rotation in one or both directions past a certain point isblocked by the ultimate stop structure;

e. a dop, mounted in part within the pivot body, ro-

tatable about an axis normal to the axis of the pivot shaft, and havingat one end a structure to firmly grip the gem stone to be cut orpolished;

f. a sensor to detect and to signal the concluding motions of the pivotbody or dop as it approaches and finally contacts the ultimate stopstructure;

g. electrical circuitry to transfer the sensor signals to a signallingdevice h. a signalling device to present to the user of the machineinformation such as the force being applied to the gem, the rate ofcutting, or the distance remaining before a desired surface or shape ofthe gem is reached.

2. A gem cutting and polishing machine, as claimed in claim 1, whereinthe sensor is comprised of one or more strain gages.

3. A gem cutting and polishing machine, as claimed in claim 1, whereinthe sensor comprises a flexible, longitudinal member, affixed at or nearone end to the pivot body support structure and situated so as to becontacted and flexed by a portion of the pivot body or of the dop duringthe concluding movements of the pivot body or dop leading up to thepivot body or dop contacting the ultimate stop structure, and aplurality of strain gages attached to the flexible member to detect andsignal deflections of the member.

4. A gem cutting and polishing machine, as claimed in claim 1, whereinthe sensor is comprised of one or more proximity sensors.

5. A gem cutting and polishing machine, as claimed in claim 1, whereinthe sensor is comprised of a proximity sensor, secured to the pivot bodysupport structure, and situated so as to be approached and finallycontacted by a magnetized portion of the pivot body or dop or by amagnet affixed to the pivot body or dop, as the pivot body or dopapproaches and finally contacts the ultimate stop structure.

6. A gem cutting and polishing machine, comprising:

a. a horizontal base;

b. a flat, rotatable disc or lap, mounted upon and parallel to the base,for mounting selectable abrasive surfaces;

0. a vertical adjustment support subassembly, substantially longitudinalin shape, mounted upon the base with longitudinal axis normal to thebase, adjustable in position on the base in directions parallel to thebase plane, and finely adjustable in height above the base plane;

d. a protractor support member, slidably mounted on the verticaladjustment support subassembly;

e. a protractor, consisting of a circular segment mounted by means ofthe protractor support member in a plane normal to the base plane;

f. a saddle block, mounted slidably upon the protractor, a portion ofsaid saddle block serving as an ultimate stop structure;

g. a pivot shaft, mounted upon the saddle block, with the axis of thepivot shaft parallel to the base plane;

h. a pivot body, mounted rotatably upon the pivot shaft in such a waythat its rotation in one or both directions past a certain point isblocked by the ultimate stop structure;

i. a dop, mounted in part Within the pivot body, rotatable about an axisnormal to the axis of the pivot shaft, and having at one end a structureto firmaly grip the gem stone to be cut or polished;

j. a sensor to detect and to signal the concluding motions of the pivotbody or dop as it approaches and finally contacts the ultimate stopstructure;

k. electrical circuitry to transfer the sensor signals to a signallingdevice l. a signalling device to present to the user of the machineinformation such as the force being applied to the gem, the rate ofcutting, or the distance remaining before a desired surface or shape ofthe gem is reached.

7. A gem cutting and polishing machine, as claimed in claim 6, whereinthe sensor is comprised of one or more strain gages.

8. A gem cutting and polishing machine, as claimed in claim 6, whereinthe sensor comprises a flexible, longitudinal member, affixed at or nearone end to the pivot body support structure and situated so as to becontacted and flexed by a portion of the pivot body or of the dop duringthe concluding movements of the pivot body or dop leading up to thepivot body or dop contacting the ultimate stop structure, and aplurality of strain gages attached to the flexible member to detect andsignal deflections of the member.

9. A gem cutting and polishing machine, as claimed in claim 6, whereinthe sensor is comprised of one or more proximity sensors.

10. A gem cutting and polishing machine, as claimed in claim 6, whereinthe sensor is comprised ofa proximity sensor, secured to the pivot bodysupport structure, and situated so as to be approached and finallycontacted by a magnetized portion of the pivot body or dop or by amagnet affixed to the pivot body or dop, as the pivot body or dopapproaches and finally contacts the ultimate stop structure.

1. A gem cutting and polishing machine, comprising: a. a base; b. a flatrotatable disc or lap, mounted upon the base, for mounting selectableabrasive surfaces; c. a pivot body support structure, mounted upon thebase, comprising in turn;
 1. a pivot shaft with axis parallel to the lapplane;
 2. an ultimate stop structure;
 3. a structure which supports theultimate stop structure and pivot shaft, and which can be adjusted tocontrol the height of the pivot shaft above the lap and the anglebetween the lap plane and an axis running from the pivot shaft to theultimate stop structure; d. a pivot body, mounted rotatably upon thepivot shaft in such a way that its rotation in one or both directionspast a certain point is blocked by the ultimate stop structure; e. adop, mounted in part within the pivot body, rotatable about an axisnormal to the axis of the pivot shaft, and having at one end a structureto firmly grip the gem stone to be cut or polished; f. a sensor todetect and to signal the concluding motions of the pivot body or dop asit approaches and finally contacts the ultimate stop structure; g.electrical circuitry to transfer the sensor signals to a signallingdevice h. a signalling device to present to the user of the machineinformation such as the force being applied to the gem, the rate ofcutting, or the distance remaining before a desired surface or shape ofthe gem is reached.
 2. an ultimate stop structure;
 2. A gem cutting andpolishing machine, as claimed in claim 1, wherein the sensor iscomprised of one or more strain gages.
 3. a structure which supports theultimate stop structure and pivot shaft, and which can be adjusted tocontrol the height of the pivot shaft above the lap and the anglebetween the lap plane and an axis running from the pivot shaft to theultimate stop structure; d. a pivot body, mounted rotatably upon thepivot shaft in such a way that its rotation in one or both directionspast a certain point is blocked by the ultimate stop structure; e. adop, mounted in part within the pivot body, rotatable about an axisnormal to the axis of the pivot shaft, and having at one end a structureto firmly grip the gem stone to be cut or polished; f. a sensor todetect and to signal the concluding motions of the pivot body or dop asit approaches and finally contacts the ultimate stop structure; g.electrical circuitry to transfer the sensor signals to a signallingdevice h. a signalling device to present to the user of the machineinformation such as the force being applied to the gem, the rate ofcutting, or the distance remaining before a desired surface or shape ofthe gem is reached.
 3. A gem cutting and polishing machine, as claimedin claim 1, wherein the sensor comprises a flexible, longitudinalmember, affixed at or near one end to the pivot body support structureand situated so as to be contacted and flexed by a portion of the pivotbody or of the dop during the concluding movements of the pivot body ordop leading up to the pivot body or dop contacting the ultimate stopstructure, and a plurality of strain gages attached to the flexiblemember to detect and signal deflections of the member.
 4. A gem cuttingand polishing machine, as claimed in claim 1, wherein the sensor iscomprised of one or more proximity sensors.
 5. A gem cutting andpolishing machine, as claimed in claim 1, wherein the sensor iscomprised of a proximity sensor, secured to the pivot body supportstructure, and situated so as to be approached and finally contacted bya magnetized portion of the pivot body or dop or by a magnet affixed tothe pivot body or dop, as the pivot body or dop approaches and finallycontacts the ultimate stop structure.
 6. A gem cutting and polishingmachine, comprising: a. a horizontal base; b. a flat, rotatable disc orlap, mounted upon and parallel to the base, for mounting selectableabrasive surfaces; c. a vertical adjustment support subassembly,substantially longitudinal in shape, mounted upon the base withlongitudinal axis normal to the base, adjustable in position on the basein directions parallel to the bAse plane, and finely adjustable inheight above the base plane; d. a protractor support member, slidablymounted on the vertical adjustment support subassembly; e. a protractor,consisting of a circular segment mounted by means of the protractorsupport member in a plane normal to the base plane; f. a saddle block,mounted slidably upon the protractor, a portion of said saddle blockserving as an ultimate stop structure; g. a pivot shaft, mounted uponthe saddle block, with the axis of the pivot shaft parallel to the baseplane; h. a pivot body, mounted rotatably upon the pivot shaft in such away that its rotation in one or both directions past a certain point isblocked by the ultimate stop structure; i. a dop, mounted in part withinthe pivot body, rotatable about an axis normal to the axis of the pivotshaft, and having at one end a structure to firmaly grip the gem stoneto be cut or polished; j. a sensor to detect and to signal theconcluding motions of the pivot body or dop as it approaches and finallycontacts the ultimate stop structure; k. electrical circuitry totransfer the sensor signals to a signalling device l. a signallingdevice to present to the user of the machine information such as theforce being applied to the gem, the rate of cutting, or the distanceremaining before a desired surface or shape of the gem is reached.
 7. Agem cutting and polishing machine, as claimed in claim 6, wherein thesensor is comprised of one or more strain gages.
 8. A gem cutting andpolishing machine, as claimed in claim 6, wherein the sensor comprises aflexible, longitudinal member, affixed at or near one end to the pivotbody support structure and situated so as to be contacted and flexed bya portion of the pivot body or of the dop during the concludingmovements of the pivot body or dop leading up to the pivot body or dopcontacting the ultimate stop structure, and a plurality of strain gagesattached to the flexible member to detect and signal deflections of themember.
 9. A gem cutting and polishing machine, as claimed in claim 6,wherein the sensor is comprised of one or more proximity sensors.
 10. Agem cutting and polishing machine, as claimed in claim 6, wherein thesensor is comprised of a proximity sensor, secured to the pivot bodysupport structure, and situated so as to be approached and finallycontacted by a magnetized portion of the pivot body or dop or by amagnet affixed to the pivot body or dop, as the pivot body or dopapproaches and finally contacts the ultimate stop structure.